Surface-modified co-doped lithium-rich manganese-based positive electrode material and preparation method thereof

Abstract

The invention relates to a surface-modified co-doped lithium-rich manganese-based positive electrode material and a preparation method thereof. The surface-modified co-doped lithium-rich manganese-based positive electrode material comprises a bulk phase part and a surface part, the bulk phase part is a cation co-doped lithium-rich manganese-based material, the chemical formula is Li < 1.2 > Ni < 0.17 > Co < 0.16-x > M < x > Ru < y > Mn < 0.47-y > O < 2 >, in the formula, M is at least one of V, Cr and Fe, x is more than or equal to 0.06 and less than or equal to 0.14, and y is more than or equal to 0.05 and less than or equal to 0.2; the surface part is a selenium-halogen composite modified layer coating the bulk phase part in situ, contains selenide and lithium halide, and is formed by heat treatment of a bulk phase material, a selenium source and a halogen source in an inert atmosphere. The positive electrode material provided by the invention has excellent structural stability and high lithium ion diffusion coefficient, has good interface compatibility with halide electrolyte, and has high energy density and long cycle stability when being used in a halide all-solid-state battery.

Description

Technical Field

[0001] This invention belongs to the field of all-solid-state battery technology, specifically relating to a surface-modified co-doped lithium-rich manganese-based cathode material and its preparation method. Background Technology

[0002] All-solid-state batteries (ASSBs), which contain no liquid electrolyte, offer high safety and energy density, making them a suitable energy system for electric vehicles and large-scale energy storage. The energy density of ASSBs largely depends on the cathode material; traditional layered cathode materials, such as LiCoO2 and LiNi, are commonly used. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) has almost reached the limit of its specific capacity; at the same time, its low operating voltage also fundamentally limits the energy density of solid-state batteries. Therefore, developing cathode materials with high specific capacity and high operating voltage has become the focus of research on all-solid-state batteries.

[0003] Lithium-rich manganese-based materials (LRMs) also possess transition metal cations (Ni... 2+ / Co 3+ ) and oxygen anion (O 2- The redox reaction of ) has a larger discharge specific capacity (≥250 mA·h·g) -1 and higher energy density (≥1000 W·h·g) -1 Currently, the most studied lithium-rich manganese-based cathode materials with high discharge specific capacity include Li. 1.2 Ni 0.2 Mn 0.6 O2, Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, Li 1.2 Ni 0.17 Co 0.16 Mn 0.47O2 and other substances, when applied to solid-state batteries, can not only improve the energy density of solid-state batteries but also effectively avoid the capacity decay problem caused by the dissolution of transition metal cations in the cathode material into the electrolyte. However, lithium-rich manganese-based cathodes suffer from irreversible oxygen release and incompatibility at the cathode / electrolyte interface caused by the oxidation of the electrolyte by escaping oxygen species. This severely damages the layered structure of lithium-rich manganese-based materials and the stability of the cathode / electrolyte interface, worsens interfacial mass transport, and further increases interfacial resistance. Simultaneously, the low electronic conductivity of lithium-rich manganese-based materials and the irreversible degradation of the interfacial structure during cycling further lead to poor kinetic behavior. These problems greatly limit the application and development of lithium-rich manganese-based cathode materials in all-solid-state batteries.

[0004] To address the aforementioned issues, strategies such as surface coating, sulfidation, and bulk element doping have been proven to stabilize lattice oxygen and construct rapid and stable lithium-ion transport channels at the cathode / electrolyte interface. For example, sodium (Na) doping acts as a "pillar," stabilizing the layered structure of lithium-rich manganese-based materials while also promoting lithium-ion transport (Advanced Energy Materials, 2016, 6(6): 1501914). For instance, a polysulfide anion-enriched surface layer can form a protective layer, improving the interfacial stability of the cathode / electrolyte (Advanced Materials, 2022, 34(11): 2109564). These strategies have improved the stability of the layered structure of lithium-rich manganese-based materials to some extent and promoted lithium-ion transport, but further improvements are needed, and the problems of cathode / electrolyte interface degradation and poor electrochemical reaction reversibility still exist. Summary of the Invention

[0005] In view of the poor stability of the layered structure, poor reversibility of electrochemical reactions, and capacity decay caused by incompatibility at the cathode / electrolyte interface in existing lithium-rich manganese-based cathode materials, this invention provides a surface-modified co-doped lithium-rich manganese-based cathode material and its preparation method. This invention uses Li... 1.2 Ni 0.17 Co 0.16 Mn 0.47 Using O2 (LNCM) material as a substrate, variable-valence transition metals M (V, Cr, or Fe) and Ru are co-doped with each other in a specific ratio to partially replace Co and Mn, respectively. The surface is then subjected to selenium halide composite modification to form a bulk cation-co-doped, surface-modified lithium-rich manganese-based cathode material. This lithium-rich manganese-based cathode material exhibits excellent structural stability and a high lithium-ion diffusion coefficient, as well as good interfacial compatibility with halide electrolytes. All-solid-state batteries assembled with halide electrolytes from this material demonstrate excellent high energy density and good long-cycle stability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A surface-modified co-doped lithium-rich manganese-based cathode material comprises a bulk phase and a surface phase; the bulk phase is a cation-co-doped lithium-rich manganese-based material with the general chemical formula Li. 1.2 Ni 0.17 Co 0.16-x M x Ru y Mn 0.47-y O2, where M is any one of V, Cr, and Fe, 0.06≤x≤0.14, 0.05≤y≤0.2; the surface portion is an in-situ coated selenium halide composite modified layer on the bulk phase portion, the selenium halide composite modified layer contains selenide and lithium halide, and is formed by heat treatment of the bulk material with selenium source and halogen source under an inert atmosphere.

[0008] Preferably, M is Cr.

[0009] Preferably, 0.08≤x≤0.12, 0.1≤y≤0.15.

[0010] Furthermore, the thickness of the selenium halide composite modified layer is 3–8 nm.

[0011] Further, the selenide is a mixture of Li2Se and RuSe, and optionally, CoSe is also present; the lithium halide is LiCl and / or LiF.

[0012] Furthermore, in the preparation of the selenium halide composite modified layer, the mass ratio of the bulk material to the selenium source and the halogen source is 10:(0.5~1.5):(1~2).

[0013] Further, the selenium source is selenium powder, and the halogen source is an ammonium halide, selected from at least one of NH4Cl and NH4F; and / or

[0014] The inert atmosphere is nitrogen and / or argon, and the temperature conditions for the heat treatment are: calcination at 500-600℃ for 1-3 hours.

[0015] The surface-modified co-doped lithium-rich manganese-based cathode material in this invention has a layered structure and is based on Li 1.2 Ni 0.17 Co 0.16 Mn 0.47Using O2 (LNCM) material as a substrate, a bulk material co-doped with variable-valence transition metals M (V, Cr, or Fe) and Ru in a specific ratio is first prepared to partially replace Co and Mn, respectively. Then, the surface of the bulk material is modified with selenium halides. The transition metals M and Co have similar ionic radii, and M's partial substitution of Co reduces lattice strain. The variable-valence Ru has a slightly larger ionic radius than Mn, and its partial substitution of Mn appropriately expands the interlayer spacing, acting as a "pillar." Both M and Ru are variable-valence metals that can participate in redox reactions, contributing to capacity. Simultaneously, the introduction of M and Ru increases the heterogeneity of the transition metal layer, thus improving structural flexibility and ultimately increasing structural stability and capacity. The bulk material obtained after the above cation co-doping modification is then further modified with selenium halides through heat treatment of the bulk material with a selenium source and a halogen source under an inert atmosphere, forming an in-situ selenium halide composite modification layer coating the bulk phase. Halogen sources such as NH4Cl and NH4F can consume residual alkali on the surface (Li2CO3 / LiOH) to form LiCl and LiF, which not only improve interfacial lithium-ion transport but also exhibit good compatibility with halide electrolytes. Simultaneously, the introduction of selenium sources partially forms products such as Li2Se, CoSe, and RuSe on the surface. These products possess electronic conductivity far exceeding that of oxides, thus mitigating the problem of low intrinsic electronic conductivity in cathode materials. In summary, the combined effects of variable-valence metals M and Ru, along with surface selenium-halide composite modification, ultimately yield a lithium-rich manganese-based cathode material with uniform co-doped bulk cations and surface modification. This material exhibits excellent structural stability, a high lithium-ion diffusion coefficient, and good interfacial compatibility with halide electrolytes.

[0016] Secondly, the present invention also provides a method for preparing the above-mentioned surface-modified co-doped lithium-rich manganese-based cathode material, comprising the following steps:

[0017] (S1) Press Li 1.2 Ni 0.17 Co 0.16-x M x Ru y Mn 0.47-y The stoichiometric ratio of O2 is used to dissolve the chelating agent and metal salts containing Li, Ni, Co, M, Ru, and Mn in water to form a mixed solution. Then, the pH of the mixed solution is adjusted to 7.0-8.0 using a pH adjuster, and then heated and evaporated under stirring to obtain a gel. The molar ratio of the chelating agent to the total metal ions is (2-4):1, and the total metal ions are composed of Li, Ni, Co, M, Ru, and Mn ions.

[0018] (S2) The gel was subjected to low-temperature heat treatment, high-temperature calcination, and pulverization in air in sequence to obtain the bulk material Li. 1.2 Ni0.17 Co 0.16-x M x Ru y Mn 0.47-y O2;

[0019] (S3) The bulk material Li 1.2 Ni 0.17 Co 0.16-x M x Ru y Mn 0.47-y O2, selenium source, and halogen source are added to a dispersion medium and heated to evaporate under stirring to obtain a mixed powder. The mixed powder is then heat-treated to obtain a surface-modified co-doped lithium-rich manganese-based cathode material.

[0020] Further, in step (S1), the chelating agent is at least one of oxalic acid, citric acid, and ethylenediaminetetraacetic acid; the metal salt is a metal acetate, nitrate, or halide; and the pH adjuster is ammonia, sodium bicarbonate, or triethanolamine.

[0021] Further, in step (S2), the low-temperature heat treatment is held at 150-200℃ for 3-6 hours; the high-temperature calcination is calcined at 900-1100℃ for 12-20 hours; and the pulverization is performed by air jet milling or ball milling until the particle size D50 is 300-600 mesh.

[0022] Thirdly, the present invention also provides an all-solid-state battery comprising a positive electrode sheet assembled from the above-mentioned surface-modified co-doped lithium-rich manganese-based positive electrode material, a halide solid electrolyte, and a negative electrode material.

[0023] Furthermore, the halide solid electrolyte is a lithium indium halide, such as Li3InCl6, Li 2.7 In 0.7 Hf 0.3 Cl6, Li3InCl 5.8 F 0.2 .

[0024] The anode material is not specifically limited, such as Li-In alloy anode or silicon-carbon anode.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention uses Li 1.2 Ni 0.17 Co 0.16 Mn 0.47Using O2 (LNCM) material as a substrate, Co and Mn are partially substituted by variable-valence transition metals M (V, Cr, or Fe) and Ru in a specific ratio, followed by surface selenium halide composite modification, to prepare a lithium-rich manganese-based cathode material with uniformly co-doped bulk cations and surface modification. This lithium-rich manganese-based cathode material exhibits excellent structural stability and a high lithium-ion diffusion coefficient, as well as good interfacial compatibility with halide electrolytes.

[0027] 2. The surface-modified co-doped lithium-rich manganese-based cathode material prepared in this invention has excellent electrochemical performance, and it exhibits high energy density and long cycle stability when used in halide all-solid-state batteries. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of an all-solid-state battery.

[0029] Figure 2 This is a high-resolution transmission electron microscope image of the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1.

[0030] Figure 3 The image shows the EDS elemental mapping of the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1.

[0031] Figure 4 The XPS spectrum of the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1 is shown.

[0032] Figure 5 SEM images of LNCM and the lithium-rich manganese-based cathode materials prepared in Examples 1, 2, and 5.

[0033] Figure 6 The XRD patterns are of LNCM and the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1.

[0034] Figure 7 The interlayer spacing is between LNCM and the oxygen layer of the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1.

[0035] Figure 8 The first charge-discharge curves of the halide all-solid-state battery assembled with LNCM and the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1 are shown.

[0036] Figure 9 The rate performance of a halide all-solid-state battery assembled with LNCM and the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1 at different current densities is shown in the figure.

[0037] Figure 10The graph shows the cycle performance of a halide all-solid-state battery assembled with the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1 under conventional load.

[0038] Figure 11 Cyclic performance of halide all-solid-state battery assembled with lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1 under high load. Detailed Implementation

[0039] The present invention will be described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0040] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0041] Example 1

[0042] M is Cr, x = 0.1, y = 0.1.

[0043] (S1) Press Li 1.2 Ni 0.17 Co 0.06 Cr 0.1 Ru 0.1 Mn 0.37 To prepare a solution, nickel acetate tetrahydrate ((CH3COOH)2Ni·4H2O), cobalt acetate tetrahydrate ((CH3COOH)2Co·4H2O), manganese acetate tetrahydrate ((CH3COOH)2Mn·4H2O), and chromium nitrate nonahydrate (Cr(NO3)3·9H2O) were dissolved in deionized water. Citric acid was then weighed and dissolved in the above solution at a molar ratio of citric acid to total metal ions of Li, Ni, Co, Cr, Ru, and Mn ions to form a mixed solution. The total metal ions consisted of Li, Ni, Co, Cr, Ru, and Mn ions. The pH of the mixed solution was adjusted to 7.5 using ammonia, and the solution was then heated in a 70°C water bath with stirring until a gel was obtained.

[0044] (S2) The gel was placed in a forced-air drying oven and kept at 180℃ for 3 hours, then placed in a muffle furnace and calcined at 950℃ for 15 hours at a rate of 10℃ / min. After calcination, it was naturally cooled to room temperature. The calcined material was then removed and air-jet pulverized to 400-500 mesh to obtain the bulk material Li. 1.2 Ni 0.17 Co 0.06 Cr 0.1 Ru 0.1 Mn 0.37 O2.

[0045] (S3) The bulk material Li 1.2 Ni0.17 Co 0.06 Cr 0.1 Ru 0.1 Mn 0.37 O2, selenium powder, and NH4Cl were mixed evenly at a mass ratio of 10:0.5:1 and placed in a muffle furnace. The mixture was then calcined at 500°C for 2 hours under a nitrogen atmosphere to obtain a surface-modified co-doped lithium-rich manganese-based cathode material, denoted as LNCCRM@Se / Cl.

[0046] Example 2

[0047] The rest is the same as in Example 1, except that the values ​​of x and y are different: x = 0.06, y = 0.05, and correspondingly step (S1) is performed according to Li. 1.2 Ni 0.17 Co 0.1 Cr 0.06 Ru 0.05 Mn 0.32 The ingredients are prepared according to the stoichiometric ratio of each element corresponding to O2.

[0048] Example 3

[0049] The rest is the same as in Example 1, except that the values ​​of x and y are different: x = 0.08, y = 0.10, and correspondingly step (S1) is performed according to Li. 1.2 Ni 0.17 Co 0.08 Cr 0.08 Ru 0.1 Mn 0.37 The ingredients are prepared according to the stoichiometric ratio of each element corresponding to O2.

[0050] Example 4

[0051] The rest is the same as in Example 1, except that the values ​​of x and y are different: x = 0.12, y = 0.15, and correspondingly step (S1) is performed according to Li. 1.2 Ni 0.17 Co 0.04 Cr 0.12 Ru 0.15 Mn 0.32 The ingredients are prepared according to the stoichiometric ratio of each element corresponding to O2.

[0052] Example 5

[0053] The rest is the same as in Example 1, except that the values ​​of x and y are different: x = 0.14, y = 0.2, and correspondingly step (S1) is performed according to Li. 1.2 Ni 0.17 Co 0.02 Cr 0.14 Ru 0.2 Mn 0.27The ingredients are prepared according to the stoichiometric ratio of each element corresponding to O2.

[0054] Example 6

[0055] The rest is the same as in Example 1, except that the type of M in step (S1) is different; M is V, and correspondingly, in step (S1) it is according to Li. 1.2 Ni 0.17 Co 0.06 V 0.1 Ru 0.1 Mn 0.37 The ingredients were prepared by mixing the elements according to their stoichiometric ratios corresponding to O2. The resulting lithium-rich manganese-based cathode material is denoted as LNCVRM@Se / Cl.

[0056] Example 7

[0057] The rest is the same as in Example 1, except that the type of M in step (S1) is different; M is Fe, and correspondingly, in step (S1) it is Li. 1.2 Ni 0.17 Co 0.06 Fe 0.1 Ru 0.1 Mn 0.37 The ingredients are prepared according to the stoichiometric ratio of each element corresponding to O2; in step (S3), NH4F is used to replace NH4Cl by mass. The resulting lithium-rich manganese-based cathode material is denoted as LNCFRM@Se / F.

[0058] Example 8

[0059] The rest is the same as in Example 1, except that the mass ratio of bulk material to selenium powder and NH4Cl in step (S3) is 10:1.5:2.

[0060] Comparative Example 1

[0061] The rest is the same as in Example 1, except that: there is no Ru, that is, only Cr is doped, and correspondingly, in step (S1) Li is doped according to the chemical formula 1.2 Ni 0.17 Co 0.06 Cr 0.1 Mn 0.47 The ingredients are prepared according to the stoichiometric ratio of each element corresponding to O2.

[0062] Comparative Example 2

[0063] The rest is the same as in Example 1, except that: there is no Cr, that is, only Ru is doped, and correspondingly, in step (S1) Li is doped according to the chemical formula 1.2 Ni 0.17 Co 0.16 Ru 0.1 Mn 0.37 The ingredients are prepared according to the stoichiometric ratio of each element corresponding to O2.

[0064] Comparative Example 3

[0065] The rest is the same as in Example 1, except that the type of M is different; M is Ti, and correspondingly, in step (S1) it is calculated according to the chemical formula Li. 1.2 Ni 0.17 Co 0.06 Ti 0.1 Ru 0.1 Mn 0.37 The ingredients are prepared according to the stoichiometric ratio of each element corresponding to O2.

[0066] Comparative Example 4

[0067] The rest is the same as in Example 1, except that step (S3) is omitted, that is, the bulk material Li obtained by step (S2) is... 1.2 Ni 0.17 Co 0.06 Cr 0.1 Ru 0.1 Mn 0.37 O2 is used as the positive electrode material.

[0068] Comparative Example 5

[0069] The rest is the same as in Example 1, except that selenium powder is not used in step (S3), specifically:

[0070] (S1) Same as Example 1;

[0071] (S2) Same as Example 2;

[0072] (S3) The bulk material Li 1.2 Ni 0.17 Co 0.06 M 0.1 Ru 0.1 Mn 0.37 O2 and NH4Cl were mixed evenly at a mass ratio of 10:1.5 and placed in a muffle furnace. The mixture was then calcined at 500°C for 2 hours under a nitrogen atmosphere to obtain a surface-modified co-doped lithium-rich manganese-based cathode material, denoted as LNCCRM@Cl.

[0073] Comparative Example 6

[0074] The rest is the same as in Example 1, except that NH4Cl is not used in step (S3), specifically:

[0075] (S1) Same as Example 1;

[0076] (S2) Same as Example 2;

[0077] (S3) The bulk material Li 1.2 Ni 0.17 Co 0.06M 0.1 Ru 0.1 Mn 0.37 O2 and selenium powder were mixed evenly at a mass ratio of 10:1 and placed in a muffle furnace. The mixture was then calcined at 500°C for 2 hours under a nitrogen atmosphere to obtain a surface-modified co-doped lithium-rich manganese-based cathode material, denoted as LNCCRM@Se.

[0078] Application examples

[0079] The lithium-rich manganese-based cathode materials prepared in the above examples and comparative examples were used in halide all-solid-state batteries. The lithium-rich manganese-based cathode material Li prepared in Example 1 was used as an example. 1.2 Ni 0.17 Co 0.06 M 0.1 Ru 0.1 Mn 0.37 O 1.8 Cl 0.2 For example, the battery assembly process is as follows:

[0080] (1) 60 mg of sulfide solid electrolyte (Li 5.5 PS 4.5 Cl 1.5 Add 60 mg of halide solid electrolyte (Li3InCl6) to the solid-state battery mold and hold it under 1t pressure for 5 min; then press 60 mg of halide solid electrolyte (Li3InCl6) onto the surface of the sulfide solid electrolyte layer and apply 2t pressure for 5 min to obtain the composite solid electrolyte layer.

[0081] (2) The lithium-rich manganese-based cathode material LNCCRM@Se / Cl, the halide solid electrolyte (Li3InCl6), and the conductive agent (Multi-wall carbon nanotubes, MWCNTs) prepared in Example 1 were mixed in a mass ratio of 57:30:13 and manually ground for 40 min to obtain composite cathode powder; then 5 mg of composite cathode powder was uniformly dispersed on the surface of the halide solid electrolyte layer in step (1), and a pressure of 3t was applied and held for 10 min to obtain a cathode-electrolyte layer bilayer structure;

[0082] (3) A battery is prepared using Li-In alloy as the negative electrode. Specifically, an indium foil with a diameter of 10 mm and a thickness of 100 μm is pressed onto the surface of the electrolyte layer (i.e., the sulfide solid electrolyte layer) in the positive electrode-electrolyte layer double-layer structure. Then, a lithium foil with a diameter of 5 mm and a thickness of 100 μm is pressed onto the indium foil to obtain a three-layer structure of positive electrode-electrolyte layer-negative electrode, thus obtaining an all-solid-state battery (see schematic diagram of the all-solid-state battery structure as shown in Figure 1). Figure 1 (As shown); Finally, the battery is fixed to the stainless steel shell, a pressure of 1t is applied and held for 5 minutes, thus completing the assembly of all batteries.

[0083] Other embodiments and comparative examples assemble all-solid-state batteries according to the above method, the difference being that the lithium-rich manganese-based cathode material in step (2) is replaced.

[0084] Testing and Analysis

[0085] 1. Structural performance

[0086] The high-resolution transmission electron microscope (TEM) image of the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1 is shown in Figure 2. Figure 2 As can be seen from the images, the lithium-rich manganese-based cathode material LNCCRM@Se / Cl has a distinct layered structure, including an inner bulk phase and a surface portion of the modified layer. The modified layer, i.e., the surface portion, is approximately 4–5 nm thick. The high-resolution transmission electron microscopy images of the cathode materials prepared in the other embodiments are similar. Figure 2 The thickness of the modified layer is approximately 3–8 nm.

[0087] The EDS elemental mapping diagram of the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1 is shown below. Figure 3 As shown, from Figure 3 It can be clearly observed that Cr and Ru are uniformly distributed in the bulk phase, while Cl and Se are mainly concentrated on the surface of the particles, i.e., the surface part.

[0088] The XPS spectrum of the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1 is shown below. Figure 4 As shown, Figure 4 The fitting peaks located at binding energies of 577.2 eV and 586.9 eV correspond to Cr 3+ The fitting peaks at binding energies of 579.5 eV and 588.9 eV are attributed to Cr. 6+ XPS spectroscopy indicates that Cr 3+ and Cr 6+ Coexisting in LNCCRM@Se / Cl, Cr 6+ The content is higher. The fitting peaks at binding energies of 464.4 eV and 463.7 eV in the figure correspond to Ru, respectively. 3+ With Ru 4+ .

[0089] In summary Figure 2 , Figure 3 , Figure 4 It can be concluded that the prepared lithium-rich manganese-based cathode material includes a bulk phase and a surface phase. The bulk phase is a Cr and Ru co-doped lithium-rich manganese-based material, and the surface phase is coated with a Cl and Se modified layer of the bulk phase, with a thickness of about 3 to 8 nm.

[0090] SEM images of LNCM and the lithium-rich manganese-based cathode materials prepared in Examples 1, 2, and 5 are shown below. Figure 5 As shown, from Figure 5 As can be seen, the original LNCM consists of irregular nanoparticles with a size of 400–500 nm. As the Cr and Ru content in LNCCRM@Se / Cl increases, the particle size gradually decreases. This may be because the introduction of Cr and Ru elements generates more nucleation sites, which promotes crystal nucleation and thus prevents particle growth during the synthesis process.

[0091] The XRD patterns of LNCM and the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1 are shown below. Figure 6 As shown, the main diffraction peaks of LNCM and LNCCRM@Se / Cl can be attributed to a two-phase composite, which consists of a layered α-NaFeO2 structure with R-3m space group and a Li2MnO3 phase with C2 / m space group. In particular, the weak diffraction peaks appearing in the 20°-25° range belong to the Li2MnO3 phase, which is related to the superlattice structure of LiMn6 in its transition metal layer. That is, the co-doping of Cr and Ru and surface modification did not destroy the layered structure of the material. XRD refinement results show that Cr and Ru occupy Co and Mn sites, respectively. At the same time, compared with LNCM, the (003) characteristic peak of LNCCRM@Se / Cl shifts to a smaller angle, indicating that Cr and Ru have been successfully doped into the lattice of the material. According to the XRD pattern and formula I LiO2 =2C hex Z ox -1 / 3C hex (C hex Z is the numerical value of the lattice constant c. ox The interlayer spacing between oxygen layers can be calculated by taking the oxygen atom positions at the 6c site along the c-axis. The interlayer spacing between the oxygen layers of LNCM and the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1 is shown below. Figure 7 As shown, the co-doping of Cr and Ru increases the interlayer spacing between oxygen layers, thereby reducing the energy barrier for ion diffusion and thus improving the diffusion ability of lithium ions during charging and discharging.

[0092] In summary, the cathode material obtained in the embodiments of the present invention is a lithium-rich manganese-based cathode material with uniform co-doping of bulk cations and surface modification. This lithium-rich manganese-based cathode material still maintains a layered structure, and the interlayer spacing between oxygen layers is increased.

[0093] 2. Electrochemical performance testing

[0094] The all-solid-state battery prepared above was subjected to constant current charge-discharge testing using a LAND CT2001A battery testing system. Specifically, the test voltage range was 1.4–4.2 V, and the current density was 1C = 200 mAh / g. The lithium-ion diffusion coefficient in the composite cathode was measured using galvanostatic intermittent titration techniques (GITT). In this process, relaxation in the cathode material originates from lithium-ion diffusion. The diffusion coefficient was calculated using the following equation:

[0095] D GITT =(4 / πτ)(n m V m / S) 2 (ΔE s / ΔE t ) 2

[0096] In the formula, τ represents the pulse current relaxation time, and n m V is the molar value of the active material. m The molar volume of the active material is represented by S, which is the contact area between the positive electrode and the solid electrolyte, and ΔE is the molar volume of the active material. s The voltage response under the action of a pulse current, ΔE t This is due to the voltage change caused by constant current discharge.

[0097] The lithium-ion diffusion coefficients of the lithium-rich manganese-based cathode materials prepared in each embodiment and comparative example are shown in Table 1.

[0098] Table 1 Lithium-ion diffusion coefficient

[0099]

[0100]

[0101] As can be seen from Table 1, the substrate material Li, compared with the blank example, 1.2 Ni 0.17 Co 0.16 Mn 0.47 Compared to O2, the lithium-rich manganese-based cathode material prepared in the embodiments of the present invention has a significantly higher lithium-ion diffusion coefficient.

[0102] The first charge-discharge curves of the halide all-solid-state battery assembled with LNCM and the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1 are shown in Figure 8. Its rate performance at different current densities is shown in the following figures. Figure 9 As shown, under normal load (laboratory conditions, 0.6 mA·h / cm), 2 Cycling performance at 0.5C is as follows Figure 10 As shown. From Figure 8It can be seen that the halide all-solid-state battery assembled with LNCCRM@Se / Cl has a higher initial coulombic efficiency and smaller voltage polarization, proving that the lithium-rich manganese-based cathode material LNCCRM@Se / Cl enhances the redox reversibility of anionic oxygen. From Figure 9 As can be seen, at all current densities, the reversible specific capacity of LNCCRM@Se / Cl is higher than that of the LNCM-assembled halide all-solid-state battery. Table 2 shows the test results of the first-cycle reversible specific capacity of each embodiment and comparative example at 0.5C.

[0103] The all-solid-state halide battery assembled from the lithium-rich manganese-based cathode material LNCCRM@Se / Cl prepared in Example 1 was tested under high load (simulating real-world usage scenarios, 3 mA·h / cm). 2 Cyclic performance at 0.1C is as follows Figure 11 As shown in the figure, it still exhibits a high reversible specific capacity under high load, with an initial reversible specific capacity of 177.2 mAh / g; and after 80 cycles under high load, the capacity retention rate still reaches approximately 87.2%. Table 2 shows the test results of the initial reversible specific capacity and capacity retention rate after 80 cycles for each embodiment and comparative example under high load at 0.1C.

[0104] Table 2 Electrochemical Performance

[0105]

[0106] As shown in Table 2, the halide all-solid-state battery assembled with the lithium-rich manganese-based cathode material prepared in this embodiment of the invention exhibits a significant improvement in cycle capacity retention under both conventional and high loads. This indicates that the lithium-rich manganese-based cathode material prepared in this embodiment of the invention possesses good structural stability and good interfacial compatibility between the cathode material and the electrolyte; simultaneously, its specific capacity is also improved. Combining the aforementioned structural analysis and the data in Table 1, the possible reasons are as follows: Firstly, by co-doping M (V, Cr, or Fe) and Ru to partially substitute Co and Mn, the layered structure of the R-3m space group is stabilized, thereby effectively suppressing the irreversible evolution of the volumetric structure during charge and discharge, and improving the lithium-ion diffusion coefficient; simultaneously, both M and Ru are variable-valence metals that can participate in redox reactions, providing a certain capacity contribution. Secondly, the co-doping of M (V, Cr, or Fe) and Ru expands the interlayer spacing between oxygen layers, further improving the lithium-ion diffusion coefficient. Thirdly, the selenium halide composite surface modification generates a composite interface layer on the surface of the cathode material that possesses both high interfacial stability and high electronic conductivity. This interface layer not only addresses the compatibility issue between the cathode material and the halide electrolyte but also improves the low intrinsic electronic conductivity of the cathode material. The combined effect of these three aspects results in halide all-solid-state batteries assembled from lithium-rich manganese-based cathode materials exhibiting high energy density, particularly high cycle capacity retention. In contrast, halide all-solid-state batteries assembled from cathode materials in Comparative Examples 1-3 show poor cycle capacity retention and specific capacity. While halide all-solid-state batteries assembled from cathode materials in Comparative Examples 4-6 exhibit better specific capacity, their cycle capacity retention is poor.

[0107] This invention provides a surface-modified co-doped lithium-rich manganese-based cathode material and its application in halide solid-state batteries. Its contribution to the prior art lies in improving the layered structure stability of lithium-rich manganese-based cathode materials, increasing their lithium-ion diffusion coefficient, and solving the capacity decay problem caused by the incompatibility between lithium-rich manganese-based cathode materials and electrolytes. The all-solid-state battery assembled with the halide electrolyte has excellent high energy density and good long-cycle stability.

Claims

1. A surface-modified co-doped lithium-rich manganese-based cathode material, characterized in that, It comprises a bulk phase and a surface phase; the bulk phase is a cation-co-doped lithium-rich manganese-based material with the chemical formula Li. 1.2 Ni 0.17 Co 0.16- x M x Ru y Mn 0.47-y O2, where M is at least one of V, Cr, and Fe, 0.06≤x≤0.14, 0.05≤y≤0.2; the surface portion is an in-situ coated selenium halide composite modified layer on the bulk phase portion, the selenium halide composite modified layer contains selenide and lithium halide, and is formed by heat treatment of the bulk material with selenium source and halogen source under an inert atmosphere.

2. The surface-modified co-doped lithium-rich manganese-based cathode material according to claim 1, characterized in that, M stands for Cr.

3. The surface-modified co-doped lithium-rich manganese-based cathode material according to claim 1, characterized in that, 0.08≤x≤0.12, 0.1≤y≤0.

15.

4. The surface-modified co-doped lithium-rich manganese-based cathode material according to claim 1, characterized in that, The thickness of the selenium halide composite modified layer is 3–8 nm.

5. The surface-modified co-doped lithium-rich manganese-based cathode material according to claim 1, characterized in that, The selenide is a mixture of Li2Se and RuSe, and optionally, CoSe is also present; the lithium halide is LiCl and / or LiF.

6. The surface-modified co-doped lithium-rich manganese-based cathode material according to claim 1, characterized in that, In the preparation of the selenium halide composite modified layer, the mass ratio of the bulk material to the selenium source and the halogen source is 10:(0.5~1.5):(1~2); Preferably, the selenium source is selenium powder, and the halogen source is an ammonium halide salt, selected from at least one of NH4Cl and NH4F; and / or The inert atmosphere is nitrogen and / or argon, and the temperature conditions for the heat treatment are: calcination at 500-600℃ for 1-3 hours.

7. The method for preparing the surface-modified co-doped lithium-rich manganese-based cathode material according to any one of claims 1-6, characterized in that, Includes the following steps: (S1) Press Li 1.2 Ni 0.17 Co 0.16-x M x Ru y Mn 0.47-y The stoichiometric ratio of O2 is used to dissolve the chelating agent and metal salts containing Li, Ni, Co, M, Ru, and Mn in water to form a mixed solution. Then, the pH of the mixed solution is adjusted to 7.0-8.0 using a pH adjuster, and then heated and evaporated under stirring to obtain a gel. The molar ratio of the chelating agent to the total metal ions is (2-4):1, and the total metal ions are composed of Li, Ni, Co, M, Ru, and Mn ions. (S2) The gel was subjected to low-temperature heat treatment, high-temperature calcination, and pulverization in air in sequence to obtain the bulk material Li. 1.2 Ni 0.17 Co 0.16-x M x Ru y Mn 0.47-y O2; (S3) The bulk material Li 1.2 Ni 0.17 Co 0.16-x M x Ru y Mn 0.47-y O2 is mixed evenly with selenium and halogen sources and then subjected to heat treatment to obtain surface-modified co-doped lithium-rich manganese-based cathode materials.

8. The preparation method according to claim 1, characterized in that, In step (S1), the chelating agent is at least one selected from oxalic acid, citric acid, and ethylenediaminetetraacetic acid; the metal salt is a metal acetate, nitrate, or halide; the pH adjuster is ammonia, sodium bicarbonate, or triethanolamine; and / or In step (S2), the low-temperature heat treatment is held at 150-200℃ for 3-6 hours; the high-temperature calcination is calcined at 900-1100℃ for 12-20 hours; and the pulverization is performed by air jet milling or ball milling until the particle size D50 is 300-600 mesh.

9. An all-solid-state battery, characterized in that, It includes a positive electrode sheet, a halide solid electrolyte, and a negative electrode material assembled from the surface-modified co-doped lithium-rich manganese-based positive electrode material as described in any one of claims 1-6.

10. The all-solid-state battery according to claim 9, characterized in that, The halide solid electrolyte is lithium indium halide.

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